As known in the state of the art, a fibrous web is wound into rolls by means of many different types of winders, for example, two-drum winders, in which a fibrous web is wound into a roll, while supported on two winding drums, through a nip between one winding drum and a fibrous web that is being formed. The web can be passed to the two-drum winder either from above, i.e. from above the winding drum to the nip between the winding drum and the fibrous web roll forming the winding nip, or from below, so that the web is passed from below the winding drum to the winding nip between the winding drum and the fibrous web roll that is being formed.
Primarily three types of two-drum winders are known from the state of the art: winders having winding drums which are hard, steel surfaced; winders in which the rear winding drum or both winding drums are soft surfaced, for example, rubber surfaced; and the winder marketed by the Metso Paper, Inc. under the trademark WinBelt®, in which a belt arrangement disposed around two guide rolls is used as a winding drum.
In winding, for example, center winding is also used in which the web roll that is building up is supported at its center, and the fibrous web is wound into a web roll through a nip between a winding drum and the web roll being formed.
As known from the state of the art, when controlling the structure of a fibrous web roll, above all its hardness, it has been affected, among other things, by changing the tension of the web being wound, by regulating the torque differential between the winding drums in a two-drum winder and by regulating center drive or surface traction in a center winder. In addition, the structure of the fibrous web roll has been affected by means of friction, for example, by selection of the winding drum coating.
It has been possible to wind rolls of a slightly larger diameter on prior-art two-drum winders that use a soft surface drum as one or both winding drums as compared with two-drum winders that use hard winding drums with a steel surface, because a soft surface tightens the roll more than a hard surface without giving rise to winding defects. However, when using soft surface winding drums, one problem can be that the soft surface may have tightened the roll even too much.
When a soft surface drum is used in winding, the tightening effect of the nip on the web increases, with the result that it may become a problem that the tightening effect increases too much, so that the roll becomes too tight and the surface sheets of the roll may break on a conveyor or during transport.
In the applications known today, the radial distribution of tension inside a roll in the running direction of the web is controlled by means of three winding parameters (Kenneth G. Frye, Winding, p. 13, FIG. 17, Tappi Press, 1990):    1. Regulating the tension of the web being wound just before a windup.    2. Regulating winding force. The winding force is the tightening of the sheet caused by torque differential in the outermost layer of the roll.    3. Regulating the radial nip load in the nips acting in connection with winding, for example, roll, winding drum, rider roll nips, and the like.
In brief, it may be stated that due to the effect of winding parameters the tension of the web just before a windup changes into wound-on-tension WOT (Wound-On-Tension i.e. the machine direction tension of the web in the outermost layer of the web roll that is building up). This wound-on-tension determines the internal tension distribution of the roll being formed.
Because of the physical limitations of the value ranges of the above-mentioned winding parameters, in windups it often becomes necessary to strengthen or weaken the WOT value attainable by the winding parameters.
In other words, the three winding parameters described above have physical limitations setting limits to where their effect can be used. Additional control possibilities are needed for control of the roll structure.
Furthermore, when using a center winder, in some situations there is a need to regulate separately one component-web winding process at a particular station, in which connection there is a need to find a larger range of regulation for this winding operation while not touching the control parameters of the other component-web winding parameters.